Bulimia nervosa (BN) and related eating disorders involving binge eating (e.g., Eating Disorder not Otherwise Specified, EDNOS; Binge Eating Disorder, BED) are serious mental health problems, particularly among young adult women but increasingly also among men. BN and its spectrum variants are associated with adverse long-term health and mental health outcomes. These disorders also are associated with elevated health services utilization, yet these services rarely target the eating disorder (ED) specifically. Cognitive- Behavioral Therapy (CBT), offered by trained professionals with specific expertise, is considered the treatment of choice f or BN and has also been shown to be effective in treating BED. Studies have found, however, that this evidence-based treatment reaches only a minority of individuals with an ED: few individuals receive care specifically for an ED, and when they do, most therapists use treatments other than CBT. Experts have called for the development of a more disseminable form of CBT as an important step within a model of treatment that progresses from minimal interventions to increasingly complex treatments. Several studies have reported the successful use of CBT-based Guided Self-Help (GSH) treatments for BN and BED, but the data are limited by small sample sizes, a restricted range of patients, and very brief follow-up. Finally, in light of the low rates of treatment seeking, the stepped care approach should include a proactive attempt to reach ED patients. The overall aim of t he proposed study is to determine the acceptability and effectiveness of CBT-GSH when delivered to a community population of women and men with a severe binge eating disorder following a large-scale outreach (screening) effort. Specifically, the study aims to determine the clinical effectiveness of CBT-GSH in the treatment of BN, BED and related EDNOS; subsidiary aims are to examine the acceptability of the CBT-GSH intervention t o potential participants and the cost-effectiveness of CBT-GSH relative to usual clinical care in a health maintenance organization. We propose to screen a random sample of 30,000 adults (ages 18 to 35) for binge eating disorders, and enroll an estimated sample of 285 of those women and men with BN, BED or EDNOS in a randomized clinical trial of CBT-GSH. The primary outcome will be change in binge eating. Secondary outcomes will include changes in associated eating pathology (e.g., body image disturbance), associated psychopathology (e.g., depression), functional impairment, body mass index, and health services use. The proposed study will answer the question whether CBT- GSH is an effective early step intervention for the treatment of binge eating disorders.